The present invention relates to a process for dyeing a textile material with indigo and an arrangement for conducting the process.
By means of this process a textile thread dyed with indigo is produced which subsequently allows a fabric named denim fabric to be prepared with which items such as jeans etc. are made.
Indigo is one of the oldest known dyes and has been used for centuries to dye textiles such as cotton.
European patent 692,042 describes a process for dyeing a textile fabric containing cellulose with indigo, in which an aqueous solution of leuco-indigo prepared by catalytic hydrogenation is used, the latter being converted into pigment form by oxidation in air after being applied on the textile fabric.
U.S. Pat. No. 4,283,198 describes a continuous process for dyeing cellulose fibers with indigo, wherein the fibers are passed through a series of soaking tanks containing a liquor of leuco-indigo, sodium hydrosulphite and sodium hydroxide.
U.S. Pat. No. 3,457,022 describes a process of dyeing cotton fibers with indigo, in which the indigo is applied at a temperature of between 65.degree. C. and 80.degree. C. to the threads and the indigo is then applied at temperatures below 40 C.
Denim dyed with indigo has the disadvantage that it fades with washing. In recent years it has even been the fashion to wear faded jeans and the industry has developed processes and equipment to follow this fashion, in which fading of the fabric was accentuated and promoted by enabling the warp thread to fade. The method used for the dyeing facilitates fading and aging. However, every fashion is short-lived and only lasts for a time.